When her sister vanishes on her own wedding day, Pauline is forced to take her place as the bride of the cold, enigmatic billionaire William. Their marriage comes with one bizarre condition: a weekly "Sunday Ritual" where he teaches her, step by step, the intimate acts of a married couple. What begins as a clinical lesson in a kiss quickly spirals into a consuming, addictive passion that Pauline cannot resist, binding her to a man she was never meant to marry—until the day her missing sister returns, threatening to shatter their forbidden, Sunday-born love.